1. Field of the Invention
The present invention relates to battery chargers.
2. Related Art
Portable electric and electronic products are powered by batteries. Increasingly, such products are being designed to use specially configured batteries rather than standard batteries. Because these specially configured batteries can be relatively expensive, typically they are recharged rather than replaced. Because these specially configured batteries often remain coupled to their corresponding products while being charged, which can preclude use of these products during the charging process, there is a desire to complete the charging process in a reasonably short period of time.
However, charging a battery too quickly can damage it. Therefore, battery chargers usually divide the charging process into a constant current procedure and a constant voltage procedure. A constant current procedure is performed during the earlier portion of the charging process and prevents the battery from being charged by current at a damaging rate. A constant voltage procedure is performed during the later portion of the charging process and allows the battery to be charged to its rated voltage.
Circuits designed to implement constant current procedures have been closed loop circuits. Usually, such circuits include capacitors to maintain stability. This increases the amount of power such circuits consume and the area that they occupy. What is needed is a battery charger circuit that implements a constant current procedure, but consumes relatively little power and occupies a relatively small area.